The present invention relates generally to free piston engine pumps and, more particularly, to variable energy rate and acceleration-deceleration controls for free piston engine pumps.
A free piston engine pump differs from the usual piston engine driven pump in that the reciprocating movement of the piston is not first transmitted to a crankshaft to convert linear movement to rotary movement and then back to linear movement by means of a pump swash plate to drive the pump piston. Instead, a direct linear drive connection is provided between the engine piston and pump piston for effecting linear movement thereof. Eliminating the linear-to-rotary crankshaft elements and rotary-to-linear pump swash plate results in a substantial reduction in size and weight of the pump and also greatly improves the efficiency thereof. There are also other corollary and independent advantages of free piston engine pumps, as is well known.
One example of a free piston engine pump is disclosed in commonly assigned copending U.S. Patent Application Ser. No. 842,494, filed Oct. 17, 1977. In the free piston engine pump disclosed therein plural hydraulic piston areas or hydraulic pressures are suitably valved to properly "phase" such areas or pressures during the engine stroke to minimize the inertia-storage of energy required to match the natural variation of energy (work) of the internal combustion cycle to obtain smooth operation. A relatively high energy or work rate phase occurs at the beginning of the power stroke during the gas expansion cycle in the engine which drives the engine piston and, thus, the pump piston. Then, there is at least one intermediate phase, during which the work rate is lower than the initial one, and a relatively high output work rate at the end of the power stroke. The high work rate phase at the end of the power stroke causes rapid deceleration at the end of the stroke and thus effects a higher ratio of average piston speed to peak speed, which tends to reduce cycle time without incurring the efficiency losses that accompany higher piston speeds. Return of the pump piston and the engine piston in a return or compression stroke is accomplished by an input of fluid from the hydraulic reservoir and/or accumulator returning the pistons to initial positions ready for the next power stroke. Preferably during the return stroke non-uniform return stroke energy is provided to the free piston engine pump, with the piston momentum carrying the piston through the latter portion of the return stroke while fluid is supplied to the pump from a reservoir to replenish the pump with fluid prior to the next power stroke.